Add a basic Django model generator.

Due to limitations of Django the schema must only have the `default`
module. Also all link properties and multi properties are forbidden
since they produce models without a unique `id` (or other primary key)
column. Django cannot properly handle updates to that.

Added tests for the generated Django models.

gel/_testbase.py

@@ -25,6 +25,7 @@
 import inspect
 import json
 import logging
+import pathlib
 import os
 import re
 import subprocess
@@ -37,7 +38,8 @@
 from gel import asyncio_client
 from gel import blocking_client
 from gel.orm.introspection import get_schema_json
-from gel.orm.sqla import ModelGenerator
+from gel.orm.sqla import ModelGenerator as SQLAModGen
+from gel.orm.django.generator import ModelGenerator as DjangoModGen
 
 
 log = logging.getLogger(__name__)
@@ -630,13 +632,13 @@ def adapt_call(cls, result):
         return result
 
 
-class SQLATestCase(SyncQueryTestCase):
-    SQLAPACKAGE = None
+class ORMTestCase(SyncQueryTestCase):
+    MODEL_PACKAGE = None
     DEFAULT_MODULE = 'default'
 
     @classmethod
     def setUpClass(cls):
-        # SQLAlchemy relies on psycopg2 to connect to Postgres and thus we
+        # ORMs rely on psycopg2 to connect to Postgres and thus we
         # need it to run tests. Unfortunately not all test environemnts might
         # have psycopg2 installed, as long as we run this in the test
         # environments that have this, it is fine since we're not expecting
@@ -648,24 +650,34 @@ def setUpClass(cls):
 
         class_set_up = os.environ.get('EDGEDB_TEST_CASES_SET_UP')
         if not class_set_up:
-            # Now that the DB is setup, generate the SQLAlchemy models from it
-            spec = get_schema_json(cls.client)
             # We'll need a temp directory to setup the generated Python
             # package
-            cls.tmpsqladir = tempfile.TemporaryDirectory()
-            gen = ModelGenerator(
-                outdir=os.path.join(cls.tmpsqladir.name, cls.SQLAPACKAGE),
-                basemodule=cls.SQLAPACKAGE,
-            )
-            gen.render_models(spec)
-            sys.path.append(cls.tmpsqladir.name)
+            cls.tmpormdir = tempfile.TemporaryDirectory()
+            sys.path.append(cls.tmpormdir.name)
+            # Now that the DB is setup, generate the ORM models from it
+            cls.spec = get_schema_json(cls.client)
+            cls.setupORM()
+
+    @classmethod
+    def setupORM(cls):
+        raise NotImplementedError
 
     @classmethod
     def tearDownClass(cls):
         super().tearDownClass()
         # cleanup the temp modules
-        sys.path.remove(cls.tmpsqladir.name)
-        cls.tmpsqladir.cleanup()
+        sys.path.remove(cls.tmpormdir.name)
+        cls.tmpormdir.cleanup()
+
+
+class SQLATestCase(ORMTestCase):
+    @classmethod
+    def setupORM(cls):
+        gen = SQLAModGen(
+            outdir=os.path.join(cls.tmpormdir.name, cls.MODEL_PACKAGE),
+            basemodule=cls.MODEL_PACKAGE,
+        )
+        gen.render_models(cls.spec)
 
     @classmethod
     def get_dsn_for_sqla(cls):
@@ -678,6 +690,69 @@ def get_dsn_for_sqla(cls):
         return dsn
 
 
+APPS_PY = '''\
+from django.apps import AppConfig
+
+
+class TestConfig(AppConfig):
+    default_auto_field = 'django.db.models.BigAutoField'
+    name = {name!r}
+'''
+
+SETTINGS_PY = '''\
+from pathlib import Path
+
+mysettings = dict(
+    INSTALLED_APPS=[
+        '{appname}.apps.TestConfig',
+        'gel.orm.django.gelmodels.apps.GelPGModel',
+    ],
+    DATABASES={{
+        'default': {{
+            'ENGINE': 'django.db.backends.postgresql',
+            'NAME': {database!r},
+            'USER': {user!r},
+            'PASSWORD': {password!r},
+            'HOST': {host!r},
+            'PORT': {port!r},
+        }}
+    }},
+)
+'''
+
+
+class DjangoTestCase(ORMTestCase):
+    @classmethod
+    def setupORM(cls):
+        pkgbase = os.path.join(cls.tmpormdir.name, cls.MODEL_PACKAGE)
+        # Set up the package for testing Django models
+        os.mkdir(pkgbase)
+        open(os.path.join(pkgbase, '__init__.py'), 'w').close()
+        with open(os.path.join(pkgbase, 'apps.py'), 'wt') as f:
+            print(
+                APPS_PY.format(name=cls.MODEL_PACKAGE),
+                file=f,
+            )
+
+        with open(os.path.join(pkgbase, 'settings.py'), 'wt') as f:
+            cargs = cls.get_connect_args(database=cls.get_database_name())
+            print(
+                SETTINGS_PY.format(
+                    appname=cls.MODEL_PACKAGE,
+                    database=cargs["database"],
+                    user=cargs["user"],
+                    password=cargs["password"],
+                    host=cargs["host"],
+                    port=cargs["port"],
+                ),
+                file=f,
+            )
+
+        models = os.path.join(pkgbase, 'models.py')
+        gen = DjangoModGen(out=models)
+        gen.render_models(cls.spec)
+
+
 _lock_cnt = 0
 
 

gel/orm/__init__.py

@@ -0,0 +1,7 @@
+import unittest
+
+# No tests here, but we want to skip the unittest loader from attempting to
+# import ORM packages which may not have been installed (like Django that has
+# a few custom adjustments to make our models work).
+def load_tests(loader, tests, pattern):
+    return tests

gel/orm/cli.py

@@ -23,7 +23,8 @@
 
 from gel.codegen.generator import _get_conn_args
 from .introspection import get_schema_json
-from .sqla import ModelGenerator
+from .sqla import ModelGenerator as SQLAModGen
+from .django.generator import ModelGenerator as DjangoModGen
 
 
 class ArgumentParser(argparse.ArgumentParser):
@@ -65,7 +66,6 @@ def error(self, message):
     "--mod",
     help="The fullname of the Python module corresponding to the output "
          "directory.",
-    required=True,
 )
 
 
@@ -74,13 +74,23 @@ def main():
     # setup client
     client = gel.create_client(**_get_conn_args(args))
     spec = get_schema_json(client)
+    generate_models(args, spec)
+
 
+def generate_models(args, spec):
     match args.orm:
         case 'sqlalchemy':
-            gen = ModelGenerator(
+            if args.mod is None:
+                parser.error('sqlalchemy requires to specify --mod')
+
+            gen = SQLAModGen(
                 outdir=args.out,
                 basemodule=args.mod,
             )
             gen.render_models(spec)
+
         case 'django':
-            print('Not available yet. Coming soon!')
+            gen = DjangoModGen(
+                out=args.out,
+            )
+            gen.render_models(spec)

gel/orm/django/gelmodels/__init__.py

@@ -0,0 +1,3 @@
+import django
+
+__version__ = "0.0.1"

gel/orm/django/gelmodels/apps.py

@@ -0,0 +1,31 @@
+from django.apps import AppConfig
+
+
+class GelPGModel(AppConfig):
+    name = "gel.orm.django.gelmodels"
+
+    def ready(self):
+        from django.db import connections, utils
+
+        gel_compiler_module = "gel.orm.django.gelmodels.compiler"
+
+        # Change the current compiler_module
+        for c in connections:
+            connections[c].ops.compiler_module = gel_compiler_module
+
+        # Update the load_backend to use our DatabaseWrapper
+        orig_load_backend = utils.load_backend
+
+        def custom_load_backend(*args, **kwargs):
+            backend = orig_load_backend(*args, **kwargs)
+
+            class GelPGBackend:
+                @staticmethod
+                def DatabaseWrapper(*args2, **kwargs2):
+                    connection = backend.DatabaseWrapper(*args2, **kwargs2)
+                    connection.ops.compiler_module = gel_compiler_module
+                    return connection
+
+            return GelPGBackend
+
+        utils.load_backend = custom_load_backend

gel/orm/django/gelmodels/compiler.py

@@ -0,0 +1,64 @@
+from django.db.models.sql.compiler import (  # noqa
+    SQLAggregateCompiler,
+    SQLCompiler,
+    SQLDeleteCompiler,
+)
+from django.db.models.sql.compiler import (  # noqa
+    SQLInsertCompiler as BaseSQLInsertCompiler,
+)
+from django.db.models.sql.compiler import (  # noqa
+    SQLUpdateCompiler as BaseSQLUpdateCompiler,
+)
+
+
+class GelSQLCompilerMixin:
+    '''
+    The reflected models have two special fields: `id` and `obj_type`. Both of
+    those fields should be read-only as they are populated automatically by
+    Gel and must not be modified.
+    '''
+    @property
+    def readonly_gel_fields(self):
+        try:
+            # Verify that this is a Gel model reflected via Postgres protocol.
+            gel_pg_meta = getattr(self.query.model, "GelPGMeta")
+        except AttributeError:
+            return set()
+        else:
+            return {'id', 'gel_type_id'}
+
+    def as_sql(self):
+        readonly_gel_fields = self.readonly_gel_fields
+        if readonly_gel_fields:
+            self.remove_readonly_gel_fields(readonly_gel_fields)
+        return super().as_sql()
+
+
+class SQLUpdateCompiler(GelSQLCompilerMixin, BaseSQLUpdateCompiler):
+    def remove_readonly_gel_fields(self, names):
+        '''
+        Remove the values corresponding to the read-only fields.
+        '''
+        values = self.query.values
+        # The tuple is (field, model, value)
+        values[:] = (tup for tup in values if tup[0].name not in names)
+
+
+class SQLInsertCompiler(GelSQLCompilerMixin, BaseSQLInsertCompiler):
+    def remove_readonly_gel_fields(self, names):
+        '''
+        Remove the read-only fields.
+        '''
+        fields = self.query.fields
+
+        try:
+            fields[:] = (f for f in fields if f.name not in names)
+        except AttributeError:
+            # When deserializing, we might get an attribute error because this
+            # list shoud be copied first:
+            #
+            # "AttributeError: The return type of 'local_concrete_fields'
+            # should never be mutated. If you want to manipulate this list for
+            # your own use, make a copy first."
+
+            self.query.fields = [f for f in fields if f.name not in names]